I've ready numerous posts on the fourms about pumps soundling like they are pumping gravel. The otehr day when the water level was down too much, the float in the skimmer fell enough that it forced all the suction to the main drain. When this happened, the pump becomes very loud and does in fact sound like its pumping gravel. I also notice air bubbles in the pump, that are not there when pumping form the skimmer.
Its a single speed 2HP pump. From what I can tell, the main drain feeds into the skimmer, and then one line from teh skimmer to the pump.
My question is could the bubbles be from a leak, or something else? I notice the pressure at the filter is 25 when running via the skimmer, and then 15 when running the main drain (i.e. the skimmer float locked down).